Remote control system for a locomotive

ABSTRACT

A locomotive control system comprising a remote transmitter issuing RF binary coded commands and a slave controller mounted on the locomotive that decodes the transmission and operates is dependence thereof various actuators to carry into effect the commands of the ground based operator.

This application is a divisional application of U.S. application Ser.No. 08/221,704, filed on Apr. 1, 1994, now U.S. Pat. No. 5,511,749.

FIELD OF THE INVENTION

The present invention relates to an electronic system for remotelycontrolling a locomotive. The system is particularly suitable for use inswitching yard assignments.

BACKGROUND OF THE INVENTION

Economic constraints have led railway companies to develop portableunits allowing a ground based operator to remotely control a locomotiveis a switching yard. The unit is essentially a transmitter communicatingwith a slave controller on the locomotive by way of a radio link.Typically, the operator carries this unit and can perform duties such ascoupling and uncoupling cars while remaining in control of thelocomotive movement at all times. This allows for placing the point ofcontrol at the point of movement thereby potentially enhancing safety,accuracy and efficiency.

Remote locomotive controllers currently used in the industry arerelatively simple devices that enable the operator to manually regulatethe throttle and brake in order to accelerate, decelerate and/ormaintain a desired speed. The operator is required to judge the speed ofthe locomotive and modulate the throttle and/or brake levers to controlthe movement of the locomotive. Therefore, the operator must possess agood understanding of the track dynamics, the braking characteristics ofthe train, etc. in order to remotely operate the locomotive in a safemanner.

OBJECT AND STATEMENT OF THE INVENTION

An object of the invention is to provide a remote locomotive controlsystem allowing the operator to command a desired speed and respondingby appropriately controlling the throttle or brake to achieve andmaintain that speed.

Another object of the invention is to provide a remote locomotivecontrol system allowing for control of the locomotive from one of twodifferent transmitters.

Yet another object of the invention is to provide a remote locomotivecontrol system having the ability to perform a number of safetyverifications in order to automatically default the locomotive to a safestate should a malfunction be detected.

SUMMARY OF THE INVENTION

As embodied and broadly described herein the invention provides alocomotive remote control system. The system has a transmitter capableof generating a binary coded radio frequency signal representingcommands to be executed by the locomotive and a slave controller formounting on-board the locomotive. The slave controller has

-   -   a) a receiver for sensing the radio frequency signal;    -   b) a processor for receiving the radio frequency signal; and    -   c) a velocity sensor for generating data representing velocity        of the locomotive. The processor responds to the velocity sensor        and to the RF signal to actuate either one of a brake of a        locomotive or a tractive power of the locomotive in order to        attempt maintaining a requested speed.

As embodied and broadly described herein the invention also provides alocomotive control system which has

-   -   a) a transmitter for generating a binary coded RF signal; and    -   b) a slave controller mounted on-board the locomotive for        receiving that signal, the slave controller selectively        accepting commands from a first transmitter or from a second        transmitter.

As embodied and broadly described herein the invention further providesa remote control system for a locomotive which has

-   -   a) a transmitter for generating an RF binary coded signal; and    -   b) a slave controller mounted on-board the locomotive.        The slave controller includes    -   a first sensor responsive to pressure of compressed air in a        main tank of the locomotive; and    -   a second sensor responsive to flow of compressed air in a        pneumatic brake line. The slave controller responds to output of        the sensors to enable application of tractive power to the        locomotive only when a pressure in the main tank is above a        predetermined level and a flow of air in the brake line is below        a predetermined level.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the portable transmitter of the remotelocomotive control system in accordance with the invention;

FIGS. 2 and 4 are side elevational views of the portable transmitter;

FIG. 3 is a front elevational view of the portable transmitter;

FIG. 5 is a functional block diagram of the portable transmitter;

FIG. 6 is a diagram of the signal transmission protocol between theportable transmitter and a slave controller mounted on-board thelocomotive;

FIG. 7 is a functional block diagram of the slave controller mountedon-board the locomotive;

FIG. 8 is a diagram illustrating the temporal relationship between thesignal transmission and the operation of the receiver of the slavecontroller;

FIG. 9 is a diagram illustrating the temporal relationship betweensignal transmission from two portable transmitters and the operation ofthe receiver of the slave controller;

FIG. 10 is a detailed functional block diagram of the slave controllermounted on-board the locomotive;

FIG. 11 is a side elevational view of a velocity sensor for generating apulse signal whose frequency is correlated to the speed of thelocomotive;

FIG. 12 is a side elevational view of the velocity sensor shown in FIG.11;

FIG. 13 illustrates the pulse output of the velocity sensor shown inFIGS. 11 and 12;

FIGS. 14a to 14d are a flow charts of the logic implemented to controlthe speed of the locomotive;

FIGS. 15a and 15b are diagrams illustrating the variation with respectto time of the velocity of the locomotive and of variables used tocalculate a throttle or brake correction signal;

FIG. 16a is a flow chart illustrating the logic for controlling thespeed of the locomotive in a COAST speed setting;

FIG. 16b is a flow chart illustrating the logic for controlling thespeed in COAST WITH BRAKE setting;

FIGS. 17a and 17b are flow charts of the logic for transferring thecommand authority from one remote control transmitter to another; and

FIG. 18 is a flow chart of the safety diagnostic routine performed onthe braking system of the locomotive.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the annexed drawings, the locomotive control system inaccordance with the invention includes a portable transmitter 10 whichgenerates a digitally encoded radio frequency (RF) signal to conveycommands to a slave controller mounted on-board the locomotive. Theslave controller decodes the transmission and operates various actuatorson the locomotive to carry into effect the commands remotely issued bythe operator.

FIGS. 1 to 4 illustrate the physical layout of the portable transmitter10. The unit comprises a housing 12 enclosing the electronic circuitryand a battery supplying electric power to operate the system. Aplurality of manually operable levers and switches projecting outsidethe housing 12 are provided to dial-in locomotive speed, brake and hornsettings, among others.

The various controls on the portable transmitter are defined in thefollowing table:

REFER- ENCE TYPE OF NUMERAL FUNCTION ACTUATOR 14 Locomotive SpeedControl Multi-Position Lever 16 Locomotive Override Brake Multi-PositionLever Control 18 Reset Push-Button 20 Direction (Forward/Reverse/Multi-Position Switch Neutral) 22 Ring Bell/Horn Toggle Switch 24 TrainBrake Control Toggle Switch 26 Power on/Lights Dim/Bright Multi-PositionSwitch 28 Status Request Push-Button 30 Time Extend Push-Button 32Relinquish Control to Companion Push-Button Portable Transmitter

A detailed description of the various functions summarized in the abovetable is provided later in this specification.

On the top surface of the housing 12 is provided a display panel 34 thatvisually echoes the control settings of the portable transmitter 10. Thedisplay panel 34 includes an array of individual light sources 36, suchas light emitting diodes (LED), corresponding to the various operativeconditions of the locomotive that can be selected by the operator.Hence, a simple visual observation of the active LED's 36 allows theoperator to determine the current position of the controls.

FIG. 5 provides a functional diagram of the portable transmitter 10. Thevarious manually operable switches and levers briefly described aboveare constituted by electric contacts whose state of conduction isaltered when the control settings are changed. For instance, thepush-button 18, 28, 30 and 32, and the toggle switches 22 and 24 haveelectric contacts that can assume either a closed condition or as openedcondition. The multi-position levers 14 and 16, and the multi-positionswitches 20 and 26, have a set of electric contact pairs, only a singlepair being closed at each position of the lever or switch. By readingthe conduction state of the individual electric contact pairs, thecommands issued by the operator can be determined.

An encoder 38 scans at short intervals the state of conduction of eachpair of contacts. The scan results allow the encoder to assembly abinary locomotive status word that represents the requested operativestate of the locomotive being controlled. The following table providesthe number of bits in the locomotive status word required for eachfunction:

NUMBER OF BITS IN LOCOMOTIVE STATUS WORD FUNCTION 3 Locomotive SpeedControl 3 Locomotive Brake Control 1 Reset 2 Direction (Forward/Reverse/Neutral) 2 Ring Bell/Horn 3 Train Brake Control 1 Lights Dim/Bright 1Status Request 1 Time Extend 1 Relinquish Control to Companion PortableTransmitter

The locomotive status word also contains an identifier segment thatuniquely represents the transmitter designated to control thelocomotive. The purpose of this feature is to ensure that the locomotivewill only accent the commands issued by the transmitter generating theproper identifier.

Most preferably, the encoder 38 includes a microprocessor programmed tointelligently assemble the locomotive status word. The microprocessorcontinuously scans the electric contacts of the transmitter controls andrecords their state of conduction. On the basis of the identity of theclosed contacts, the program will produce the function component of thelocomotive status word which is the string of bits that uniquelyrepresents the functions to be performed by the locomotive. The programthen appends to the function component the locomotive identifiercomponent and preferably a data security code enabling the receiveron-board the locomotive to check for transmission errors.

In a different form of construction, the encoder may be constituted byan array of hardwired logic gates that generate the locomotive statusword upon actuation of the controls.

A transmitter 40 receives the locomotive status word and generates an RFsignal for transmission of the coded sequence by frequency shift keying.In essence, the frequency of a carrier is shifted to a first value tosignal a logical 1 and to a second value to signal a logical 0. Thetransmission protocol is best shown in FIG. 6. Each transmission beginswith a burst of the carrier frequency 42 for a duration of eight (8)bits (the actual time frame is established on the basis of thetransmission baud rate allowed by the equipment). Each bit of the datastream is then sent by shifting the frequency to the first or the secondvalue depending on the value of the bit, during a predetermined timeslot 44.

The transmitter 40 sends out the locomotive status word in repetition ata fixed rate selected in the range from two (2) to five (5) times persecond. By providing the transmitter with a unique repetition rate, thelikelihood of transmission errors is reduced when several portabletransmitters in close proximity broadcast control signals to individuallocomotives, as described below.

FIG. 7 provides a diagrammatic representation of the slave controllermounted on board the locomotive. The slave controller identifiedcomprehensively by the reference numeral 46 has three main components,namely a receiver unit 48, a processing unit 50 and a driver unit 52.More particularly, the receiver unit 48 senses the locomotive statusword sent out from the portable transmitter 10, decodes the transmissionand supplies the resulting binary sequence to the processing unit 50. Toachieve a reliable communication link, the receiver 48 is synchronizedwith the transmitter 40 at three different levels. First, the receivercircuitry defines a signal acceptance window than opens itself at therate at which the locomotive status word is sent out by the respectivecontrolling transmitter 40. Second, the receiver 48 will observe thefrequency value of the transmission in order to decode the binarysequence at intervals precisely corresponding to the time slots 44.Third, the acceptance window opens in phase with the signaltransmission.

The first two levels of synchronization are established through hardwaredesign, by setting the transmitter 40 and the receiver 48 to the sameperiod of transmission/reception. On the other hand, the phasing of thereceiver to the incoming locomotive status word transmission is effectedthrough observation of the burst of carrier frequency 42 that beginseach transmission cycle. The diagram in FIG. 8 graphically illustratesthe relationship between the signal transmission and the signalreception. The time line 54 shows the successive transmission of thelocomotive status word as a series of blocks 56. The activity of thereceiver 48 is shown on the time line 58. The hatched areas correspondto the time intervals during which the receiver is not listening. Attime t=0 the first locomotive status word is sent out by the transmitter40. The burst of the carrier frequency 42 sensed by the receiver 48which then activates the sequence of opening and closing of the signalacceptance window which is fully synchronized (in period and phase) withthe signal transmission.

This characteristic is particularly advantageous when severaltransmitters broadcast simultaneously control signals to differentlocomotives in close proximity to one another. By setting eachtransmitter (and the companion receiver) at a uniquetransmission/reception period, secure communication links can bemaintained even when all the transmitters use the same carrierfrequency. FIG. 9 illustrates this feature. Time line 60 shows thetransmission pattern of a first portable transmitter. The time line 62depicts the window of acceptance of the companion receiver. The numeral64 identifies the transmission pattern of a second portable transmitter.Assuming that both portable transmitters are actuated exactly at t=0,the signal received during the first opening of the window of acceptancewill be corrupted since two locomotive status word transmissions areconcurrent in time. However, the third and the seventh locomotive statusword transmissions from the first portable transmitter will be clearlyreceived since there is no overlap with the locomotive status words sentout by the second portable transmitter. Hence the purpose of providingeach transmitter with a unique signal repetition rate reduces thelikelihood of transmission conflicts.

It should be noted that the receiver 48 can, and probably will,correctly receive from time to time a locomotive status word from anunrelated transmitter. This status word will be rejected, however,because the transmitter identifier will not match the value stored inthe memory of the slave controller.

The transmitter/receiver gear of the remote locomotive control systemhas been described above in terms of function of the principal parts ofthe system and their interaction. The components and interconnections ofthe electric network necessary to carry into effect the desiredfunctions are not being specified because such details are well withinthe read of a man skilled in the art.

FIG. 10 provides a functional diagram of the processing unit 50. Acentral processing unit (CPU) 66 communicates with a memory through abus 70. A reserved portion memory 68 contains the program that directsthe CPU 66 to control the locomotive depending on the several inputsthat will be discussed later. The memory also contains a sectionallowing temporary storage of data used by the CPU when handlinghardware events.

The current locomotive status and the commands issued from the remotetransmitter are directed to the CPU through an interface 72communicating with the bus 70. The interface 72 receives input signalsfrom the following sources:

-   -   a) A speed direction sensor 74 providing locomotive velocity and        direction of movement data;    -   b) A speed sensor 76 providing solely locomotive velocity data.        The speed sensor 76 provides the CPU 66 with redundant velocity        data allowing the CPU 66 to detect a possible failure of the        main speed sensor 74.    -   c) A pressure sensor 78 observing the air pressure in the        locomotive brake system;    -   d) A pressure sensor 79 observing the air pressure in the main        reservoir;    -   e) A pressure sensor 80 observing the air pressure in the train        brake system;    -   f) A sensor 82 observing the flow rate of air in the brake        system of the train; and    -   g) The decoded locomotive status word generated by the receiver        48.

The structure of the speed/direction sensor 74 is illustrated in FIGS.11 and 12. The sensor includes a disk 84 mounted to an axle 86 of thelocomotive. When the locomotive is moving the disk 84 turns at the sameangular speed as the axle 86. The disk 84 is provided with a layer ofreflective coating 85 deposited to form on the periphery of the diskequidistant and alternating reflective zones 87 and substantiallynon-reflective zones 89. A pair of opto-electric sensors 92 and 94 aremounted in a spaced apart relationship adjacent the periphery of thedisk 84. The sensor 92 comprises an emitter 92a generating a light beamperpendicular to the plane of the disk 84, and a receiver 92b producingan electric signal when sensing the reflection of the light beam on thereflective zones 87. However, when a substantially non-reflectivesurface 89 registers with the sensor 92, the output of the receiver isnull or very low. The structure and operation of the opto-electricsensor 94 is identical to the sensor 92. Thus, the sensor 94 comprisesan emitter 94a and a receiver 94b.

The spacing between the opto-electric sensors 92 and 94 is such thatthey generate output pulses due to the periodic change in reflectivityof the disk surface, occurring at different instants in time. As bestshown in FIG. 10, and assuming that the disk 84 rotates in the counterclockwise direction, when the sensor 92 switches “on” as a result of areflective zone 87 registering with the emitter 92a and the receiver92b, the sensor 94 is still in a stable on condition and can be causedto switch off only by further rotating the disk 84.

Preferably, the disk 84 and the sensors 92 and 94 are mounted in ahermetically sealed housing to protect the assembly againstcontamination by water or dirt.

FIG. 13 illustrates the signal waveforms produced by the opto-electricsensors 92 and 94. Both outputs are pulse trains having the samefrequency but out of phase by an angle a which depends upon the spacingof the sensors 92 and 94. When the locomotive moves forward the disk 84rotates in a given direction, say clockwise. In this case, the pulsetrain from sensor 94 leads the public train from sensor 92 by angle a.When the locomotive is in reverse, then the output of sensor 92 leadsthe output of sensor 94 by angle a (this possibility is not shown inFIG. 13). The processing unit 50 observes the occurrence of the leadingpulse edges from the sensors 92 and 94 with relation to time todetermine the identity of the leading signal, which allows deriviationof the direction of movement of the locomotive.

Velocity data is derived by measuring the rate of fluctuation of thesignal form any one of sensors 92 and 92. It has been found practical todetermine the velocity at low locomotive speeds by measuring the periodof the signal. However, at higher speeds the frequency of the signal isbeing measured since the period shortens which may introducenon-negligible measurement errors.

The speed sensor 76 is similar to sensor 74 described above with twoexceptions. First, a single opto-electric sensor may be used since allthat is required is velocity data. Second, the speed sensor 76 ismounted to a different axle of the locomotive.

The pressure sensors 78 and 79 are switches mounted to the mainreservoir and to the pneumatic line that supplies working fluid to thelocomotive independent braking mechanism, and produce an electric signalin response to pressure. These sensors merely indicate the presence ofpressure, not its magnitude. In essence, each sensor produces an outputwhen the air pressure exceeds a preset level, indicating whether thereserve of compressed air is sufficient for reliable braking. Unlike thesensors 78 and 79, the pressure sensor 80 is a transducer that generatesa signal indicative of presence and magnitude of pressure in the trainbrake air line.

The airflow sensor 82 observes the volume of air circulating in thepneumatic lines of the train brake system. The results of thismeasurement along with the output of pressure sensor 78 provide anindication of the state of charge of the pneumatic network. It isconsidered normal for a long pneumatic path to experience some air leaksdue primarily to imperfect unions in pipe couplings between cars of thetrain. However, when a considerable volume of air leaks, the airflowsensor 82 enables the processing unit to sense such condition and toimplement corrective measures, as will be discussed later.

The interface 72 receives the signals produced by the sensors 74, 76,78, 79, 80, and 82 and digitizes them where required so they can bedirectly processed by the CPU 66. The locomotive status word issued bythe receiver 48 requires no conversion since it is already in the properbinary format.

The binary signals generated by the CPU 66 that control the variousfunctions of the locomotive are supplied through the bus 70 and theinterface 72. The following control signals are being issued:

-   -   a) A signal 98 to set the lights of the locomotive to off/low        intensity/high intensity. The signal is constituted by one (1)        bit, each operative condition of the locomotive lights being        represented by a different bit state;    -   b) A two (2) bit signal 100 to operate the bell or the horn of        the locomotive;    -   c) A five (5) bit signal 102 for traction control. Four bits are        used to communicate the throttle settings (only eight (8)        settings are possible) and one bit for the power contacts of the        electric traction motors;    -   d) An eight (8) bit signal 104 for train brake control. The        number of bits used allows 256 possible brake settings; and    -   e) A seven (7) bit signal 106 for independent brake control. The        number of bits used allows 128 possible brake settings.

The interface 72 will convert at least some of the signals 98, 100, 102,104, and 106 from the binary form to a different form that the device atwhich the signals are directed can handle. This is described in moredetail below.

The actuators for the lights and bell/horn are merely switches such asrelays or solid state devices that energize or de-energize the desiredcircuit. The interface 72, in response to the CPU 66 instruction to setthe lights/bell/horn in the desired operative position, will generate anelectric signal that is amplified by the driver unit 52 and thendirected to the respective relay or solid state switch.

With regard to the traction control it should be noted that mostlocomotive manufacturers will install on the diesel/electric engine asoriginal equipment a series of actuators that control the fuelinjection, power contacts and brakes among others, hence the tractionpower that the locomotive develops. This feature permits couplingseveral locomotives under control of one driver. By electrically andpneumatically interconnecting the actuators of all the locomotives, thethrottle commands the driver issues in the cab of the mother engine areduplicated in all the slave locomotives. The locomotive remote controlsystem in accordance with the invention makes use of the existingthrottle/brake actuators in order to control power. The interface 72converts the binary throttle settings issued by the CPU 66 to thestandard signal protocol established by the industry for controllingthrottle/brake actuators. This feature is particularly advantageousbecause the locomotive remote control system does not require theinstallation of any throttle/brake actuators. As in the case of thelights and bell/horn signals 98 and 100, respectively, the tractioncontrol signal 102 incoming from the interface 72 is amplified in thedriver unit 52 before being directed to the throttle/brake actuators.

The train brake control signal 104 issued by the interface 72 is aneight (8) bit binary sequence applied to a value mounted in the trainbrake circuit to modulate the air pressure in the train line thatcontrols the braking mechanism. The working fluid is supplied from amain reservoir whose integrity is monitored by the pressure sensor 79described above. The independent locomotive brake is controlled in thesame fashion with binary signal 106.

The operation of the locomotive control system will now be describedwith more detail.

SPEED CONTROL TASK

The flowchart of the speed control logic is shown in FIGS. 14a to 14d.The program execution begins by reading the velocity data generated fromsensors 74 and 76 that are mounted at different axles of the locomotive.The data gathered from each sensor is stored in the memory 68 and thencompared at step 124. If both sensors are functioning properly theyshould generate identical or nearly identical velocity values. In theevent a significant difference is noted the CPU 66 concludes that amalfunction exists and issues a command (step 126) to fully apply theindependent brake in order to bring the locomotive to a complete stop.

Assuming that no mismatch between the readings of sensors 74 and 76 isdetected, the CPU 66 will compare the observed locomotive speed with thespeed requested by the operator. The later variable is represented by astring of three (3) bits in the locomotive status word (the flowchart ofFIGS. 14a to 14d assumes that the locomotive status word has beencorrectly received, has the proper identifier and has been stored in thememory 68). The operator can select on the portable transmitter 10 eightpossible speed settings, each setting being represented by a differentbinary sequence. The speed settings are as follows:

1) STOP

2) COAST WITH BRAKE

3) COAST

4) COUPLE (1 MILE PER HOUR (MPH))

5) 4 MPH

6) 7 MPH

7) 10 MPH

8) 15 MPH

If any one of settings 4 to 8 have been selected, which require thelocomotive to positively maintain a certain speed, the CPU 66 willeffect a certain number of comparisons at steps 128 and 130 to determineif there is a variation between the actual speed and the selected speedalong with the sign of the variation, i.e. whether the locomotive isoverspeeding or moving too slowly. More particularly, if at step 128 theCPU 66 determines that the observed speed is in line with the desiredspeed no corrective measure is taken and the program execution initiatesa new cycle. On the other hand, if the actual speed differs from thesetting, the conditional test 130 is applied to determine the sign ofthe difference. Under a negative sign, i.e. the locomotive is moving tooslowly, the program execution branches to processing thread A (shown inFIG. 14b). In this program segment the CPU 66 will determine at step 132the velocity error by subtracting the actual velocity from the set pointcontained in the locomotive status word. A proportional plus derivativeplus integral algorithm is then applied for calculating throttle settingintended for reducing the velocity error to zero. Essentially the CPU 66will calculate the sum of the integral of the velocity error signal(calculated in step 145), of the derivative of the velocity error signal(calculated in step 147), and of a proportional factor (calculated instep 143). The latter is the velocity error signal multiplied by apredetermined constant. The result of this calculation provides acontrol signal that is used for modulating the throttle actuator of thelocomotive through output signal 102 of the interface 72.

FIG. 15a is a diagram illustrating the variation of the current velocitysignal, the set point, the velocity error, the velocity error integral,the velocity error derivative and velocity error proportional withrespect to time.

With reference to FIG. 14d, when the new throttle setting has beenimplemented the program execution continues to steps 134 and 136 wherethe current direction of movement and speed of the locomotive aredetermined from the reading of sensor 74. In the event the CPU 66observes a zero speed value for a time period of more than 20 seconds inspite of the fact that a tractive effort is being applied (step 138), itdeclares a malfunction and fully applies the independent locomotivebrake. Normally, when a tractive effort is applied it causes thelocomotive to accelerate. The movement, however, may occur after acertain delay following the application of the tractive effortespecially if the locomotive is pulling a heavy consist. Still, if aftera certain time period no movement is observed, some sort of malfunctionis probably present. One possibility is that both sensors 74 and 76 havefailed and register zero speed even when the locomotive is rolling. Thisis highly unlikely but not impossible. When such condition isencountered the CPU 66 immobilizes the locomotive immediately upondetermination that a fault is present.

The 20 seconds waiting period before application of the independentbrake is implemented by verifying the velocity data from sensor 74during a certain number of program execution cycles. For instance, thecurrent velocity value is compared to the velocity value observed duringthe previous execution cycle that has been stored in the memory 68. If achange is noted, i.e. the locomotive moves, then the step 138 isconsidered to have been successively passed. If, however, after 200execution cycles that require about 20 seconds to be completed, nochange with the previously observed velocity value is noted, theindependent brake is fully applied.

Assuming that motion of the locomotive is detected at step 138, theprogram proceeds to step 140 where the direction of movement of thelocomotive read from the output of sensor 74 is compared to thedirection of movement specified by the operator. This value isrepresented by a four (4) bit string is the locomotive status word. Ifthe locomotive is moving rearwardly while the operator has specified aforward movement, the CPU 66 detects a condition known as “rollback”.Such condition may occur when the locomotive is starting to moveupwardly on a grade while pulling a heavy consist. Under the effect ofgravity the train may move backward for a certain distance until thetraction system of the locomotive has been able to build-up the pullingforce necessary to reverse the movement. During a rollback condition theelectric current in the traction motors of the locomotive increasebeyond safe levels. Hence it is desirable to limit the rollback in orderto avoid damaging the hardware. The program is designed to tolerate arollback condition for no longer than 20 seconds. If the conditionpersists beyond this time period the independent brake is fully applied.The 20 seconds delay is implemented by comparing the evolution of theresults of the comparison step 140 with the results obtained during theprevious execution cycle; if the results do not change for 200 programexecution cycles that require about 20 seconds of running time on theCPU 66, a fault is declared and the brake applied.

In the case where both tests 136 and 140 are successively passed, i.e.the locomotive is moving in the selected direction, the programexecution returns to the beginning of the cycle as shown in FIG. 14a.

Referring back to step 130, if the conditional branch points towardprocessing thread B (see FIGS. 14a and 14c), which means that thelocomotive is overspeeding, then the CPU 66 will calculate at step 142the difference between the selected speed and the observed speed. Theresulting error signal is then processed by using the proportional plusderivative plus integral algorithm described above to derive a newthrottle setting. If by controlling the throttle (reducing the tractiveeffort developed by the engine) speed correction cannot be achieved, thebrake is applied. The brake is modulated by using a proportional plusderivative plus integral algorithm. FIG. 15b illustrates the brakeresponse, along with the actual brake, error, proportional, derivative,and integral signals with relation to time. The calculated brake settingis issued as binary signal 106 (see FIG. 10) that is directed to thebraking mechanism on the locomotive.

The STOP, COAST WITH BRAKE and COAST settings will now be brieflydescribed. The STOP setting, as the name implies, intends to bring andmaintain the locomotive stationary. When the CPU 66 receives alocomotive status word containing a speed setting corresponding to STOPit immediately terminates the tractive effort and applies theindependent locomotive brake at a controlled rate. The program logic toimplement the COAST and COAST WITH BRAKE services is illustrated asflowcharts in FIGS. 16a and 16b, respectively. When the multi-positionlever 14 is set to the COAST setting the program reads the velocity datafrom sensor 74 at step 144 and then compares it at step 146 to thevelocity value recorded during the previous program execution cycle. Ifthe consist accelerates under the effect of gravity down a grade (notractive effort is applied by the system in the COAST and COAST WITHBRAKE settings) the observed velocity will show an increase. The CPU 66will then apply the independent locomotive brake to slow the consist atstep 148. The brake is modulated by using a proportional plus integralplus derivative (PID) algorithm. In the event that no velocity increaseis observed the CPU 66 may set (depending upon the control signalresulting from the PID calculation) the independent brake to the releaseposition at step 150 or keep the brake at the current setting.

The next step in the program execution is a test 152 which determines ifthe speed of the consist is below 0.5 MPH. In the affirmative themovement is stopped by full application of the independent brake at step154. If the speed of the consist exceeds or is equal to 0.5 MPH then theprogram returns to step 144.

The COAST WITH BRAKE function, depicted in FIG. 16b is very similar tothe COAST service described above. The only difference is that a minimumindependent brake pressure of 15 pounds per square inch (psi) is alwaysmaintained. At step 156 the acceleration of the consist is determined bycomparison of the current velocity with a previous velocity value. If apositive acceleration is observed, such as when the consist moves down agrade, the brake pressure is increased at step 158 (the control is madeby a PID algorithm). During the next program execution cycle theacceleration is determined again. If no positive acceleration is sensedthe brake pressure is returned to 15 psi at step 160. At step 162 thevelocity of the consist is tested against the 0.5 MPH value. If thecurrent speed is less than this limit a full independent brakeapplication is effected in order to stop the consist, otherwise theprogram execution initiates a new cycle.

EXCHANGE OF COMMAND AUTHORITY BETWEEN REMOTE TRANSMITTERS

In some instances a single operator may effectively and safely control aconsist that includes a limited number of cars remaining at all timeswell within the visual range of the operator. However, when the consistis long two operators may be required, each person being physicallyclose to and monitoring one end of the train. The present inventionprovides a locomotive control system capable of receiving inputs fromthe selected one of two or more remote transmitters. In a two-operatorarrangement, each person is provided with a portable transmitter 10 ableto generate the complete range of locomotive control commands. In orderto avoid confusion, however, the slave controller on-board thelocomotive will accept at any point in time commands from a singledesignated transmitter. The only exception is a limited set of emergencyand signalling commands that are available to both operators. Thecontrol function can be transferred from one transmitter to the other byfollowing the logic depicted in the flowchart of FIGS. 17a and 17b.

Upon reception of a locomotive status word, the CPU will compare theidentifier in the word to a list of two or more possible identifiersstored in the memory 68. The list of acceptable identifiers contains theidentifiers of all the remote transmitters permitted to assume controlof the locomotive. If the identifier in the locomotive status word doesnot correspond to any one of the identifiers in the list, then thesystem rejects the word and takes no action. Otherwise, the system willdetermine what are the requested functions that the locomotive shouldperform. If the locomotive status word requests application of theemergency brake or sounding the bell or horn, then the system complieswith the request. Otherwise (step 179), if a new speed setting isrequested for example, the system will comply only if the identifier inthe locomotive status word matches a specific identifier in the listthat designates the remote transmitter currently holding the commandauthority. If this step is verified, then the locomotive executes thecommand unless the command is a request to transfer command authority toanother remote controller. The CPU 66 recognizes this request bychecking the state of the bit reserved for this function in thelocomotive status word. If the state of the bit is 1 (command transferrequested) the program execution continues at step 180 where the CPU 66will perform a certain number of safety checks to determine if thecommand transfer can be made in a safe manner. More particularly, theCPU will determine if the locomotive is stopped and if the brake safetychecks (to be described later) are verified. If the locomotive is movingor the brake safety checks fail, then no action is taken and the commandremains with the portable transmitter currently in control. If this testis passed, then the CPU will monitor the reset bit of all the locomotivestatus words received that carry an identifier in the list stored in thememory 68 (the reset bit issued by the transmitter currently holding thecontrols is not considered). If within 10 seconds of the reception ofthe request to transfer control from the current transmitter the CPUobserves a reset bit in the high position, which means that the operatorof a remote transmitter in the pool of candidates able to acquirecontrol has depressed the reset button, then the CPU 66 shifts in memorythe identifier associated with the reset bit at high to the position ofthe current control holder. From now on the CPU 66 will accept commands(except the safety related functions of emergency brake and sounding thebell/born) only from the new authority. The procedure of checking thereset bit is used for safety purposes in order to transfer the controlof the locomotive only when the target remote controller has effectivelyacknowledged acceptance of the control.

If within the 10 seconds no reset bit is set to the high position, theCPU 66 will abort the transfer function and resume normal execution ofthe program.

BRAKE SAFETY CHECKS

FIG. 18 is a flow chart of a program segment used to identify the stateof readiness of the braking system before authorizing movement of thelocomotive. When a command is received to move the locomotive forward,the CPU 66 will check the pressure in the main tank that suppliescompressed air to both the independent locomotive and to the trainbrake. If the pressure is below a preset level, the command to move thelocomotive forward is aborted and no action is taken. Asecond/verification step is required to allow movement of a locomotivewhich is a measurement of the flow rate of compressed air in the trainbrake line. The traction control signal 102 is issued only when thecompressed air flow rate is below a predetermined level. As brieflydiscussed earlier, it is normal for a train brake line to exhibit acertain leakage due to imperfect couplings in unions between cars.However, when this leakage exceeds a predetermined level, either thereis a major leak or the system is discharged and it is currently beingpumped with air. In both cases the train should not be operated forobvious safety reasons.

The scope of the present invention is not limited by the description,examples and suggestive uses herein as modification and refinements canbe made without departing from the spirit of the invention. Thus, it isintended that the present invention covers the modification andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A remote control system for a locomotive, comprising: a firsttransmitter generating a set of RF signal commands, each RF signalcommand signalling the locomotive to execute a certain function; asecond transmitter generating a set of RF signal commands, each RFsignal command from the set of said second transmitter signalling thelocomotive to execute a certain function; and a slave controllerreceiving RF commands from said first transmitter and from said secondtransmitter and assigning to each one of said first and secondtransmitters one of a command authority holder operational status and acommand authority non-holder operational status, said slave controllerbeing responsive: i) to at least one RF signal command generated by saidfirst transmitter causing the locomotive to execute a predeterminedfunction, ii) to at least one RF signal command generated by said secondtransmitter causing the locomotive to execute a predetermined function,iii) to an RF signal command other than said at least one RF signalcommand generated by a selected one of said first and secondtransmitters to cause the locomotive to perform a certain function, iv)an RF signal command other than said at least one frequency signalcommand solely generated by a transmitter having a command authorityholder operational status, and v) to a command authority relinquish RFsignal command generated by one of said first and second transmittershaving a command authority holder operational status to assign thecommand authority holder operational status to the other of said firstand second transmitters; wherein said slave controller rejects an RFcommand, other than said at least one RF signal command, issued from anon-selected one of said first and second transmitters.
 2. A remotecontrol system for a locomotive as claimed in claim 1 14, wherein saidat least one RF signal command signals said slave controller to effectapplication of braking power.
 3. A remote control system for alocomotive, comprising: a first transmitter generating a set of RFsignal commands, each RF signal command signalling the locomotive toexecute a certain function; a second transmitter generating a set of RFsignal commands, each RF signal command from the set of said secondtransmitter signalling the locomotive to execute a certain function; anda slave controller receiving RF commands from said first transmitter andfrom said second transmitter and assigning to each one of said first andsecond transmitters one of a command authority holder operational statusand a command authority non-holder operational status, said slavecontroller being responsive: i) to at least one RF signal commandgenerated by said first transmitter causing the locomotive to execute apredetermined function, ii) to at least one RF signal command generatedby said second transmitter causing the locomotive to execute apredetermined function, iii) to an RF signal command other than said atleast one RF signal command generated by a selected one of said firstand second transmitters to cause the locomotive to perform a certainfunction, iv) to an RF signal command other than said at least onefrequency RF signal command solely generated by a transmitter having acommand authority holder operational status, v) to a command authorityrelinquish RF signal command generated by one of said first and secondtransmitters having a command authority holder operational status, andvi) to a command authority acceptance RF signal command generated by theother of said first and second transmitters having a command authoritynon-holder operational status, to assign the command authority holderoperational status to the other of said first and second transmitters;wherein said slave controller rejects an RF command, other than said atleast one RF signal command, issued from a non-selected one of saidfirst and second transmitters.
 4. A remote control system for alocomotive as claimed in claim 3, wherein said at least one RF signalcommand signals said slave controller to effect application of brakingpower.
 5. A remote control system for a locomotive as claimed in claim 3wherein said at least one RF signal command is a signaling command.
 6. Aremote control system for a locomotive as claimed in claim 5 whereinsaid at least one RF signal command signals said slave controller tosound a bell or horn.
 7. A remote control system for a locomotive asclaimed in claim 3 wherein said slave controller initiates a safetycheck prior to assigning the command authority holder operational statusto the other of said first and second transmitters.
 8. A remote controlsystem for a locomotive as claimed in claim 7 wherein said safety checkincludes determining if the locomotive is stopped.
 9. A remote controlsystem for a locomotive as claimed in claim 7 wherein said safety checkincludes a brake safety check.
 10. A remote control system for alocomotive as claimed in claim 3 wherein said slave controller maintainsa list of two or more identifiers of transmitters permitted to assumethe command authority holder operational status.
 11. A remote controlsystem for a locomotive as claimed in claim 3 wherein the other of saidfirst and second transmitters acknowledges acceptance within apredetermined time period in order for the slave controller to transferthe command authority holder operational status to the other of saidfirst and second transmitters.
 12. A remote control system as defined inclaim 3, wherein said first and second transmitters generate RF signalcommands on a common carrier frequency.
 13. A remote control system fora locomotive, comprising: a first transmitter generating a set of RFsignal commands, each RF signal command signalling the locomotive toexecute a certain function; a second transmitter generating a set of RFsignal commands, each RF signal command from the set of said secondtransmitter signalling the locomotive to execute a certain function; anda slave controller receiving RF commands from said first transmitter andfrom said second transmitter and assigning to each one of said first andsecond transmitters one of a command authority holder operational statusand a command authority non-holder operational status, said slavecontroller being responsive: i) to at least one RF signal commandgenerated by said first transmitter causing the locomotive to execute apredetermined function, ii) to at least one RF signal command generatedby said second transmitter causing the locomotive to execute apredetermined function, iii) to an RF signal command other than said atleast one RF signal command generated by a selected one of said firstand second transmitters to cause the locomotive to perform a certainfunction, iv) to an RF signal command other than said at least one RFsignal command solely generated by a transmitter having a commandauthority holder operational status, and v) to a command authorityrelinquish RF signal command generated by one of said first and secondtransmitters having a command authority holder operational status toassign the command authority holder operational status to the other ofsaid first and second transmitters; wherein said slave controllerrejects an RF command, other than said at least one RF signal command,issued from a non-selected one of said first and second transmitters;and wherein said slave controller maintains a list of two or moreidentifiers of transmitters permitted to assume the command authorityholder operational status and said slave controller checks said list foran identifier designating the other of said first and secondtransmitters prior to assigning the command authority holder operationstatus to the other of said first and second transmitters.
 14. A remotecontrol system for a locomotive, comprising: a first transmittergenerating a set of RF signal commands, each RF signal commandsignalling the locomotive to execute a certain function; a secondtransmitter generating a set of RF signal commands, each RF signalcommand from the set of said second transmitter signalling thelocomotive to execute a certain function; and a slave controllerreceiving RF commands from said first transmitter and from said secondtransmitter and assigning to each one of said first and secondtransmitters one of a command authority holder operational status and acommand authority non-holder operational status, said slave controllerbeing responsive: i) to at least one RF signal command generated by saidfirst transmitter causing the locomotive to execute a predeterminedfunction, ii) to at least one RF signal command generated by said secondtransmitter causing the locomotive to execute a predetermined function,iii) to an RF signal command other than said at least one RF signalcommand generated by a selected one of said first and secondtransmitters to cause the locomotive to perform a certain function, iv)to an RF signal command other than said at least one RF signal commandsolely generated by a transmitter having a command authority holderoperational status, and v) to a command authority relinquish RF signalcommand generated by one of said first and second transmitters having acommand authority holder operational status to assign the commandauthority holder operational status to the other of said first andsecond transmitters; wherein said slave controller rejects an RFcommand, other than said at least one RF signal command, issued from anon-selected one of said first and second transmitters; and wherein theother of said first and second transmitters acknowledges acceptance ofthe command authority holder operational status prior to the slavecontroller assigning the command authority holder operation status tothe other of said first and second transmitters.
 15. A remote controlsystem for a locomotive as claimed in claim 14 wherein said at least oneRF signal command is a signaling command.
 16. A remote control systemfor a locomotive as claimed in claim 15 wherein said at least one RFsignal command signals said slave controller to sound a bell or horn.17. A remote control system for a locomotive as claimed in claim 14wherein said slave controller initiates a safety check prior toassigning the command authority holder operational status to the otherof said first and second transmitters.
 18. A remote control system for alocomotive as claimed in claim 17 wherein said safety check includesdetermining if the locomotive is stopped.
 19. A remote control systemfor a locomotive as claimed in claim 17 wherein said safety checkincludes a brake safety check.
 20. A remote control system for alocomotive as claimed in claim 14 wherein the other of said first andsecond transmitters acknowledges acceptance within a predetermined timeperiod in order for the slave controller to transfer the commandauthority holder operational status to the other of said first andsecond transmitters.